1. Field of the Invention
The present invention relates to a developing method for developing an electostatic latent image in an electrophotography or electrostatic printing, particularly to a mono-component developing method using a mono-component developer.
2. Description of the Prior Art
Generally, two-component developing methods and mono-component developing methods are known in the art for use in a developing machine. However, mono-component developing methods are often adopted in view of preventing the decrease in charging efficiency and reducing the size of image forming apparatus.
In a mono-component developing method, a toner-regulating blade is disposed to contact with a developing sleeve. By passing a mono-component developer through a gap between the developing sleeve and the toner-regulating blade, a thin toner-layer is formed on said sleeve and charged, and the thin toner-layer is directly transported to a developing area to develop an electrostatic latent image formed on an electrostatic latent image-supporting member. More specifically, the development is carried out using a mono-component developing machine, for example, as shown in FIG. 4.
Namely, the developing machine of FIG. 4 includes a driving roller 91 which is rotated and driven by a driving means (not shown) in a CCW direction, a flexible developing sleeve 92 having an inner diameter a little larger than an outer diameter of said roller is fitted on the driving roller from outside; both ends of said sleeve is pressed onto the driving roller 91 from the rear by a pressing guide 93; and a slack portion 920 of the developing sleeve 92 formed on the opposite side by said pressing is in soft contact with an electrostatic latent image-supporting member PC(photoreceptor drum in this example). Also, a toner-regulating blade 94 is in contact with the developing sleeve 92 from the same side as the pressing guide 93.
A buffer chamber 95 is disposed at the rear of the developing sleeve 92, and further a toner supplying chamber 96 is disposed at the rear thereof. A toner supplying rotary member 97 (rotating in the CCW direction) is disposed in the buffer chamber 95, and a toner stirring/supplying rotary member 98 (rotating in a CW direction, i.e. in a clockwise direction) is disposed in the toner supplying chamber 96. Further, a bottom sealing member 99 abuts a bottom surface of the developing sleeve 92 for preventing the toner from leaking to the outside of the buffer chamber 95.
According to this developing machine, a toner T introduced into the buffer chamber 95 from the toner supplying chamber 96 by rotation of the rotary member 98 is successively supplied onto a surface of the developing sleeve 92 in a toner supplying area by rotation of the toner supplying rotary member 97. Meanwhile, the sleeve 92 rotates to follow the rotation of the driving roller 91 by friction. The toner T supplied to the sleeve 92 is charged electrically by friction under a pressure from the blade 94 and held on the surface of the sleeve 92 as a thin layer of a predetermined thickness by passing through a gap between the toner-regulating blade 94 and the developing sleeve 92. The toner T is transported to a developing area that faces the photoreceptor drum PC to be subjected to development of an electrostatic latent image under a developing bias V.sub.B from a power source 921.
A residual toner T after the development passes through a gap between the sealing member 99 and the developing sleeve 92 to be returned to the buffer chamber 95 in accordance with the rotation of the sleeve 92. The toner that has returned to the buffer chamber 95 is released from the sleeve 92.
However, in such a mono-component developing method, the residual toner that has not been used for development and is remaining on the sleeve is unlikely to be completely separated in the buffer chamber due to the friction charging of the toner by the toner-regulating blade. Therefore, the toner is accumulated on the sleeve by repetition of the copying operation and receives a stress for many times by the regulating blade, whereby the toner may be smeared onto the sleeve to generate toner-filming or the toner may be fixed onto the blade to decrease the thin toner layer-forming efficiency to generate fogging on the photoreceptor, causing a problem of poor development.
Further, the stress in the above-mentioned gap causes deterioration of the toner, namely, decrease in toner particle size and separation of fluidizing agents (for example, silica) added to the toner particles, thereby decreasing the fluidity of the toner particles and deteriorating the follow-up properties of black solid image and the like. Also, since the toner particles of small particle size are especially unlikely to be separated from the sleeve, the problem of toner filming on the sleeve (referred to "sleeve filmin" hereinafter) and photoreceptor fogging will be more conspicuous by reduction of particle size of the toner particles.
With the increase in the number of small-size particles, the number of accumulated toner particles will increase. Therefore, the toner newly added to the sleeve is charged not only by the regulating blade but also by friction among the toner particles themselves, so that the number of toner particles charged in a polarity opposite to the normal charging polarity increases, resulting in deterioration of the image quality.